Jonas,
No vignetting does not go away in 4:3 aspect ration, and I should not say it goes away completely in 16-9 either. It becomes less pronounced.
Here is my take on F0.95 and F1.1 lenses -
they are very sharp and contrasty, even if not when out of the camera, Auto Levels in pp will yell great results, no more editing is necessary.
Those lenses are essential for available light portraits or with dark backgrounds, where vignetting not going to matter. Its not for studio work. Considering size of these lenses, everyone should have one of them in the camera bag.
The Switar has a little less vignetting that f0.95 lens, but still visible, but Im willing to crop. Based on my observations if you shoot at 16-9 ratio and crop the image to look like 4-3 ration your field of view will jump from 50mm to be closer to 70mm lens. And to me 70mm equivalent FOV with f0.95 is a WOW factor. (so what I have to crop a little, all of my images go through pp and 50% of them I crop anyway, not for vignetting but just for composition. You can not fix lack of detail, or chronic softness, or glare, but vignetting is bs, leica f0.95 vignettes a little as well.